Engine systems that include rotary vane engines (hereinafter referred to as “rotary vane engine systems”) possess various advantages in relation to engines such as Otto, diesel, and Sterling-cycle engines, gas turbines, and steam engines.
For example, Otto-cycle engines require a minimum fuel to air ratio to achieve combustion. The minimum fuel to air ratio at which combustion can be achieved typically results in incomplete combustion. Incomplete combustion produces relatively large amounts of carbon monoxide (CO) in the exhaust, and can necessitate the use of a catalytic converter to remove some or all of the CO form the exhaust. Rotary vane engine systems, by contrast, can operate with a combustion process that provides complete combustion with excess oxygen present in the exhaust, without the use of catalytic converters or other pollution-control devices.
Moreover, the fuel used in an Otto-cycle engine needs to be formulated so that the fuel will not combust prematurely, i.e., at a pressure or temperature lower than the operating respective pressure and temperature of the engine. Premature combustion is commonly known as “pre-ignition knock.” Pre-ignition knock can substantially reduce engine efficiency, and can damage the engine. Rotary vane engine systems are not susceptible to pre-ignition knock, and can generally use any type of fuel that releases sufficient energy during combustion to drive the rotary vane engine, including crude oil and dried wood.
Approximately one third-of the energy released in an Otto-cycle engine by the combustion of fuel can exit the engine as unused energy via the engine exhaust. Some of this energy could be recovered if the expansion ratio within the engine's cylinders could be made greater than the compression ratio. Because compression and expansion occur in the same cylinder in an Otto-cycle engine, achieving different expansion and compression ratios would require that the compression process begin under a partial vacuum. Starting the compression process under a partial vacuum, however, would substantially reducing the overall power produced by the engine. The compression and expansion processes in rotary vane engine systems, by contrast, can be performed in separate mechanical devices that readily facilitate the use of different compression and expansion ratios.
The combustion temperature in an Otto-cycle engine is relatively high, which can result in high nitrogen oxide (NOX) emissions. Because NOX is a prime contributor to smog, exhaust gas recycling and other provisions may be needed to reduce the NOX emissions to acceptable levels. Rotary vane engine systems, by contrast, can be configured so that the combustion temperature can be continuously varied, thereby facilitating lower NOX emissions and increased fuel efficiency.
The dwell time of the fuel-air mixture in an Otto-cycle engine, in general, is relatively short, particularly at high engine speeds. The short dwell time can result in unburned fuel exiting the exhaust, potentially resulting in unsatisfactory emission levels and necessitating the use of a catalytic converter or other pollution-control devices. The dwell time of the fuel in a rotary vane engine systems can be substantially longer than in an Otto-cycle engine, thereby promoting complete combustion of the fuel.
The compression ratio in typical diesel-cycle engines can be approximately 20:1. Fuel is sprayed into each cylinder after the air therein is compressed, and the resulting fuel-air mixture is combusted. Diesel engines have no throttle to limit intake the intake pressure below ambient, and the expansion ratio in a typical diesel-cycle engine is usually about equal to the compression ratio. The relatively high compression ratio in diesel engines can result in relatively high NOX emissions. The compression and expansion processes in rotary vane engine systems, as discussed above, can be performed in separate mechanical devices that readily facilitate the use of a compression ratio that is lower than the expansion ratio.
Moreover, the dwell time of the fuel-air mixture in a diesel-cycle engine is relatively short. Although additives such as cetane improvers can be introduced into the fuel to hasten the combustion process, incomplete combustion manifested as soot in the engine exhaust is common in diesel-cycle engines. The dwell time of the fuel in a rotary vane engine systems can be substantially longer than in a diesel-cycle engine, thereby promoting complete combustion of the fuel.
Diesel fuels typically have a relatively high boiling point, which can inhibit the tendency of the fuel to vaporize. Accordingly, diesel fuel is usually injected into the cylinder as a high-pressure spray to facilitate vaporization. The equipment needed to control and otherwise facilitate the fuel injection process can be relatively complex and expensive, however, due to need to vary the amount of fuel injected as the speed and timing of the engine change. Rotary vane engines, as discussed above, can generally use any type of fuel that releases sufficient energy during combustion to drive the rotary vane engine, and the relatively long dwell-time of the fuel-air mixture in rotary vane engine systems can promote complete combustion of the fuel.
Diesel and Otto-cycle engines typically require some type of liquid or air cooling. The energy transferred out of the engines as heat during the cooling process represents an energy loss. The need to cool diesel and Otto-cycle engines results in part from the use of lubricants within the engines. In particular, most lubricants degrade at the operating temperatures of a typical diesel or Otto-cycle engine, thereby necessitating engine cooling to avoid subjecting the lubricants to excessive temperatures. Rotary vane engine systems, by contrast, can operate at temperatures that are less than half the operating temperature of a typical diesel or Otto-cycle engine. Thus, the cooling requirements for rotary vane engine systems, and the energy losses associated therewith, are usually less than those of a diesel or Otto-cycle engine. Moreover, the relatively low operating temperatures of rotary vane engine systems can eliminate the need for a lubrication system in some applications.
The combustion process in steam and Sterling-cycle engines does not occur in the gas that is expanded to produce a work output. Thus, the efficiency of the heat-transfer process from the fuel to the working fluid is relatively poor. By contrast, the fuel in rotary vane engine systems is mixed and combusted with the air that is to be expanded. Thus, nearly all of the energy released from the fuel during combustion can be used to heat the working fluid.
Gas turbine engines typically use a turbine that extracts energy from a high-pressure, high-temperature gas by impulse (direction change), reaction (acceleration), or a combination thereof. The turbine typically operates at relatively high rotational speeds, to avoid excessive by-pass of the gas past the turbine blades and the accompanying energy losses. The expanding gases in rotary vane engine systems, by contrast, are typically confined by vanes that are able to effectively confine the gases at low rotational speeds.
Rotary vane engine systems may be subjected to operating conditions, e.g., torque outputs, rotational speeds, etc., that vary widely during normal operation. Although rotary vane engine systems possess substantial advantages in relation to other types of engine systems, a typical rotary vane engine system cannot operate optimally, e.g., at maximum thermal efficiency, as it operating conditions vary. Consequently, an ongoing need exists for rotary vane engine systems having operating characteristics that can be optimized as operating conditions vary.